Democratic governor candidate J.B. Pritzker said Tuesday he would seek to temporarily raise Illinois’ flat income tax rate and boost credits and deductions while lawmakers consider changing the state constitution to allow for a graduated income tax.

Pritzker, though, declined to say what that increased tax rate should be. During the primary campaign, he also didn’t say what rates should come with his favored graduated tax, which would tax people of various income levels based on how much they make. Both, he said, are subject to talks with state lawmakers.

“Just like the constitutional amendment, really you’d have to negotiate with the legislature over what those rates are and look at the budget for that year you’re putting it in place for,” Pritzker said. “So then you really couldn’t name the rates until you had that negotiating process.”

Republican Gov. Bruce Rauner repeatedly has criticized Pritzker over the lack of detail in his tax proposals. On Tuesday, Rauner’s team questioned: “When is J.B. Pritzker going to be honest with Illinoisans about how much he wants to raise their taxes?”

Rauner vetoed last year’s state income tax hike, but enough Republicans joined Democratic lawmakers to override him.

Pritzker has said his goals as governor would be expanding early childhood education, increasing funding for grade and high schools, widening tax breaks for lower-income earners and reducing the property tax burden on local homeowners. Achieving them could require a significant increase in the state income tax rate of 4.95 percent on individuals.

Illinois widely is regarded as paying a relatively low share of the funding for public grade and high schools, about 25 percent based on Illinois State Board of Education figures for the 2016-2017 school year. Instead, nearly 70 percent of schools’ money comes from local property taxes. A Civic Federation study found that $18 billion in property taxes is dedicated to local schools statewide.

Each percentage point increase in the state personal and corporate income tax rate would generate about $3.7 billion. That number also represents roughly the same amount of additional money lawmakers have guaranteed to provide to local schools over the next decade — $350 million each year — as part of a new school-aid funding formula.

Under a true graduated income tax that Prizker backs, different levels of wages are taxed at increasingly higher rates. Such a tax, like that levied by the federal government, is prohibited by the Illinois Constitution. That means lawmakers would have to send voters a proposed constitutional amendment, which couldn’t get on the ballot for consideration until 2020 at the earliest.

“It would take us about two years in total to get it all done and said, that we would have a progressive income tax,” Pritzker said at a Loop news conference.

“So in the meantime, you could have what I would describe as … an artificial progressive income tax in which we would raise the exemptions for those striving to get to the middle class, those in the middle class too, and raise the overall rate and raise the earned income tax credit at the same time — all of which would create a kind of artificial graduated income tax in the state,” he said.

Pritzker didn’t elaborate on how additional exemptions or deductions would work. He said he viewed an increase in the state’s flat-rate income tax as “only a temporary answer and that you really need the permanent answer of a constitutional amendment.”

Pritzker said it was “clear that in order to actually get a constitutional amendment passed, you really would have to make clear to the voters, who ultimately will decide about the amendment, what those rates will be and so that would result from this negotiation (with lawmakers).”